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Transition of refractive index contrast in course of grating growth.

Sabel T, Zschocher M - Sci Rep (2013)

Bottom Line: We found two steps of growth, separated by a depletion of the light diffraction.Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change.We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

View Article: PubMed Central - PubMed

Affiliation: Institute for Optics and Atomic Physics, now at Chemical Department, Technische Universität Berlin, Strasse des 17 Juni 135, Berlin, Germany. tina@physik.tuberlin.de

ABSTRACT
Studies on the dynamics of holographic pattern formation in photosensitive polymers, gaining deeper insight into the specific material transformations, are essential for improvements in holographic recording as well as in integrated optics. Here we investigate the kinetics of volume hologram formation in an organic cationic ring-opening polymerization system. The time evolution of the grating strength and the grating phase is presented. We found two steps of growth, separated by a depletion of the light diffraction. Capable to explore this growing behavior, a transition-theory of the refractive index contrast is established. Accordingly the growth curves appear to be ruled by the interplay of polymerization and diffusion. Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change. We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

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Influence of the grating period.Growth curves for various lattice spacings highlight the impact of the exposure procedure.
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f4: Influence of the grating period.Growth curves for various lattice spacings highlight the impact of the exposure procedure.

Mentions: Figure 4 shows growth curves on logarithmic time scale with grating periods of 140 nm, 2 μm, 3 μm and 7 μm respectively, whereas exposure time was 5 seconds in case of the 2 μm-grating and 15 seconds in all other cases. Very small grating periods, i.e. a high R parameter (Fig. 4 top left) results in a single growth step. The refractive index contrast is presumably negative from the very start of grating growth, with no transition taking place, due to the very short diffusion length. Diametrically opposed to this very large grating periods, i.e. a low R parameter corresponds to an exceedingly pronounced transition (Fig. 4 bottom right). A stationary balance of positive and negative change of the refractive index seems to last for several minutes before the depletion slowly starts. In between those extreme cases the intermediate behavior constitutes the characteristic two-step growth. Thereby shorter grating periods, lower viscosity and/or short exposure duration, i.e. a high R parameter results in shorter transition time. At the threshold (Fig. 4 top right) the first step of growth is only visible on a double logarithmic scale. A decrease of the R parameter by means of increasing grating periods, longer exposure duration and/or higher viscosity results in prolonged transition (Fig. 4 bottom left), i.e. increasing transition time. In particular the corresponding transition times for the intermediate growth curves (Fig. 4 top right and bottom left) are 85 s and 4000 s, respectively.


Transition of refractive index contrast in course of grating growth.

Sabel T, Zschocher M - Sci Rep (2013)

Influence of the grating period.Growth curves for various lattice spacings highlight the impact of the exposure procedure.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3757355&req=5

f4: Influence of the grating period.Growth curves for various lattice spacings highlight the impact of the exposure procedure.
Mentions: Figure 4 shows growth curves on logarithmic time scale with grating periods of 140 nm, 2 μm, 3 μm and 7 μm respectively, whereas exposure time was 5 seconds in case of the 2 μm-grating and 15 seconds in all other cases. Very small grating periods, i.e. a high R parameter (Fig. 4 top left) results in a single growth step. The refractive index contrast is presumably negative from the very start of grating growth, with no transition taking place, due to the very short diffusion length. Diametrically opposed to this very large grating periods, i.e. a low R parameter corresponds to an exceedingly pronounced transition (Fig. 4 bottom right). A stationary balance of positive and negative change of the refractive index seems to last for several minutes before the depletion slowly starts. In between those extreme cases the intermediate behavior constitutes the characteristic two-step growth. Thereby shorter grating periods, lower viscosity and/or short exposure duration, i.e. a high R parameter results in shorter transition time. At the threshold (Fig. 4 top right) the first step of growth is only visible on a double logarithmic scale. A decrease of the R parameter by means of increasing grating periods, longer exposure duration and/or higher viscosity results in prolonged transition (Fig. 4 bottom left), i.e. increasing transition time. In particular the corresponding transition times for the intermediate growth curves (Fig. 4 top right and bottom left) are 85 s and 4000 s, respectively.

Bottom Line: We found two steps of growth, separated by a depletion of the light diffraction.Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change.We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

View Article: PubMed Central - PubMed

Affiliation: Institute for Optics and Atomic Physics, now at Chemical Department, Technische Universität Berlin, Strasse des 17 Juni 135, Berlin, Germany. tina@physik.tuberlin.de

ABSTRACT
Studies on the dynamics of holographic pattern formation in photosensitive polymers, gaining deeper insight into the specific material transformations, are essential for improvements in holographic recording as well as in integrated optics. Here we investigate the kinetics of volume hologram formation in an organic cationic ring-opening polymerization system. The time evolution of the grating strength and the grating phase is presented. We found two steps of growth, separated by a depletion of the light diffraction. Capable to explore this growing behavior, a transition-theory of the refractive index contrast is established. Accordingly the growth curves appear to be ruled by the interplay of polymerization and diffusion. Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change. We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

Show MeSH
Related in: MedlinePlus